Question

(a) Describe the action of an acid buffer solution with an example.
(b) Write any five common terms in Cell Terminology.

Answer 1

(a) A buffer solution is one which maintains its pH fairly constant even upon the addition of small amounts of acid or base.
e.g., for acidic buffer $C{H}_{3}COOH+C{H}_{3}COONa$
basic buffer $N{H}_{4}OH+N{H}_{4}Cl$.
Buffer action: Let us consider the common buffer system containing acetic acid and sodium actetate.
$C{H}_{3}COOH\rightleftharpoons C{H}_{3}CO{O}^{-}+H^{+}$
$C{H}_{3}COONa\to C{H}_{3}CO{O}^{-}+N{a}^{+}$
Since, the salt is completely ionised, it provides the common ions $C{H}_{3}CO{O}^{-}$ in excess. The common ion effect suppresses the ionisation of acetic acid. This reduces the $\left[H^{+}\right]$ and pH of the solution is raised.
The pH of a buffer solution containing equimolar amounts (0.10 m) of acetic acid and sodium actetate is 4.74.
Addition of HCI: Upon the addition of HCI, the decrease of $H^{+}$ ions is counteracted by association with the excess of acetate ions to form unionised $C{H}_{3}COOH$. Thus, the added $H^{+}$ ions are neutralised and the pH of the buffer solution remains unchanged.
Addition of NaOH: When NaOH is added to the buffer solution, the additional OH ions combine with $C{H}_{3}COOH$ to give $C{H}_{3}CO{O}^{-}$ and $H_{2}O$. Thus, pH of the buffer solution is maintained almost constant.